1. Field of the Invention
The invention relates to an implantable implant having an elongate main body and a functional conductor extending in the longitudinal direction of the main body, which acts to implement a medical function of the element. Elements of this type are in particular stimulation electrode lines (sometimes also referred to in short as “electrodes”) of cardiac pacemakers or shock electrode lines of implantable defibrillators, but also catheters which contain an elongate conductive structure, or also guide wires or vascular supports (stents), in which the main body itself represents the functional conductor in the meaning of the terminology of this patent application. Furthermore, the invention relates to an electronic implant, which is typically inserted into the body using a line.
2. Description of the Related Art
Medical implants such as the listed pacemakers and defibrillators frequently have an electrical connection to the interior of the body of the patient. Such a connection is used to measure electrical signals and/or to stimulate body cells. This connection is often implemented as an oblong electrode. In the present case, electrical signals are transmitted between the implant and the electrode contacts (tips, rings, HV shock coils, sensors, inter alia) using materials having good electrical conduction.
If a system made of implant and electrode is subjected to strong interfering field (EMI, MRI), undesired misbehavior may occur, especially heating of parts of the system or electrical malfunctions (e.g., resets).
The cause of the undesired misbehavior is the interaction of the field with the oblong line structure, which forms an inductance: It acts as an antenna and receives energy from the surrounding fields. The antennae can discharge this energy on the therapeutically used lines distally to the tissue via the electrode contacts (tip, ring . . . ) or proximally to the implant.
Comparable problems also occur in other oblong conductive structures, whose proximal end is not necessarily connected to an implant (e.g., in catheters, guide wires, temporary electrodes, stents, etc.).
In recent years, countermeasures to solve the described problems have already been proposed. In addition to measures for shielding the RF energy from the electrode or the introduction of a bandpass filter into the electrode feed line (cf. U.S. Pat. No. 7,363,090 B2) a thermoswitch in the electrode feed line is also known; cf. US2009/0105789. In addition to unfavorable design properties (rigidity of the electrode), such a thermoswitch also has the disadvantages of significant hysteresis and a poorly settable and controllable temperature range and can only turn the electrode tips on or off completely, so that in the turned-off state, stimulation or derivation of signals is no longer possible. The application of this electrode for pacemaker-dependent patients is thus precluded.
The solutions from, for example, U.S. Pat. No. 7,363,090 B2 do allow a continuous electrical path to be provided for low frequencies (i.e., for the typical pacemaker function of pacing and sensing), but they are rigid in their embodiment known up to this point and impair the control capability of the electrodes significantly during implantation, so that the clinical use is put into question de facto. These known solution variants also require additional contact points not required in the typical production process of an electrode, in order to install this solution, which is implemented as a discrete element. This introduces additional risk points into the design of such an electrode.
Further approaches for solving the above-described problems are described in US 2009/0198314, which discloses suitable dimensioning and a coaxial multicore construction of a pacemaker electrode line, and in US 2009/0171421, which teaches the installation of a plurality of circuit segments spaced apart from one another having high impedance in an electrode line having coiled functional conductor. In addition, reference is made to WO 2009/049310 A1, in which multicore conductor configurations having coaxial construction or elongate conductors in parallel configuration are also proposed as a configuration for suppressing the alternating current propagation along elongate implants.